Variable ratio gear drive



March 22, 1949. H. c. .cooMBEs 2,465,201

VARIABLE RATIO GEAR DRIVE Filed Feb. is, 1946 Patented Mar. 2 2 1949 VARIABLE RATIO GEAR DRIVE Hector Charles Coombes, Sydney, New South Wales, Australia Application February 15, 1946, Serial No. 647,884 In Australia November 6, 1945 7 Claims. (Cl. 74-781) This invention relates to variable ratio gear drives such as are used for winches, motor vehicles and other mechanisms requiring a variable torque: load drive, and the object thereof is to provide a transmission which will automatically select the most advantageous transmission speed ratio, within its limits of operation, according to the load to be overcome at any instant.

Within its limits of low and high transmission ratio, any ratio whatever can be selected as the gear is infinitely variable and is not limited by a series of fixed transmission ratios. It is a characteristic of the gear that it will select the highest possible ratio which will overcome the applied load.

In order to describe the invention in detail reference is made to the accompanying drawings which depict an embodiment thereof as applied to winch work, and in which:

Fig. 1 is a perspective View, and

Fig. 2 is a longitudinal cross-sectional elevation of the gear.

The base 3 carries pedestal bearings 4 and 5. Driving shaft 6 is mounted directly in bearing 4 and extends through bearing 5, and driving coupling gear 'I is mounted on its outer end.

The cage plates 8, 9 of an epicyclic gear are rotatably mounted about driving shaft 6, and are united as a unit by distance bolts III, III. A driving spur gear I I is keyed to driving shaft 6 directly inside cage plate 8, and a driven spur gear I2 having an integral extended sleeve I3 is rotatably mounted about shaft 6, directly inside cage plate 9. Sleeve I3 rotatably extends through cage plate 9 and bearing 5, and on its outer end is keyed driven coupling gear I4.

Driving spur gear II is connected with driven spur gear I2 through two duplicate sets of planetary gears mounted in the cage and each comprising a planet gear I5 meshing with spur gear II and a planet gear I6 meshing with spur gear I2, both planet gears being keyed to a planet shaft I1 rotatably mounted in cage plates 8 and 9. Planet gears I5 are of the same diameter as driving spur gear II.

Exteriorly of cage plate 8 is located the back drive to the control mechanism. Each shaft I1 is fitted with a gear I8 meshing with an idler I9 rotatably mounted in cage plate 8, which idlers mesh with a control gear 20 on a sleeve 2I rotatably mounted on driving shaft 6.

Control gear 2!] drives the control mechanism in the manner now described. A ratchet Wheel 22 is rigidly mounted on sleeve 2|, and through pawls 23, 23 drives (in known manner and in one direction) a worm wheel 24 rotatably mounted on sleeve 2|. The worm wheel 24 drives a worm 25 secured on control shaft 26 which is carried in bearings 27, 28. A brake drum 29 is secured on shaft 26 and its rotation is controlled by a brake shoe 30 operated. by a hydraulic ram 3I of conventional type.

Driving spur gear II is also designed for direct engagement with driven spur gear I2 to lock the gear in the direct drive condition. Driving shaft 6 is movable axially by a lever 32 pivoted at 33 to the frame, and having a finger 34 rotatably engaged between collars 35, 35 on shaft 6. When shaft 6 is moved axially it carries only the main driving gear I and the driving spur gear II with it, which latter gear is formed with dogs 36, 36 which engage in recesses 3'1, 3'! of sleeve l3 carrying driven spur gear I2, 50 that these two spur gears are locked together.

The operation of the reduction gear is as follows:

Assume that the transmission gear is not locked in the direct drive condition, that clockwise torque from a prime mover is applied to the driving gear 1, and the load is coupled to clockwise driven gear I4.

The clockwise rotation of the driving shaft 6 (in the direction of arrow 4| in Fig. 1) is transmitted, by driving spur gear II and planetary gears I5, I5 to planetary shafts I1, I! and planetary gears I6, I6 as an anticlockwise rotation. As driven gear I4, and hence driven spur gear I2, are coupled to the load and consequently resist rotation, the tendency of planet gears I6, I6 is to walk anticlockwise around spur gear I2, carrying the cage with them in the direction of arrow 42 in Fig. 1.

The anticlockwise rotation of planetary shafts I1, I! and their attached gears I8, I8 is transmitted (through idlers l9, I9) the control gear '20 and its sleeve 2I as an anticlockwise rotation. From sleeve 2| this rotation is conveyed by the ratchet 22 and pawls 23 to the worm wheel 24, which rotates worm 25, its shaft 26 and control brake drum 29.

In this condition the cage may rotate anticlockwise in an unimpeded manner, which would result in the absence of drive to the final driven gear I4. To restrain the cage, brake 30 is adjustably applied to brake drum 29 by hydraulic ram 3|. The braking required is relatively slight (and hence capable of delicate control), because of the high gear ratio between worm wheel '24 and worm 25.

As the restraint on brake drum 29 is increased, so the freedom of rotation of control gear 29 is progressively impeded. Since, however, driving spur gear II continues to rotate planet shafts I1, I! and their gears I8, I8, which in turn continue to rotate idlers I9, I9, these idlers on ac-- count of this continued rotation commence to wa clockwise around the partially restrained control gear 20. This Walking of the idlers commences the clockwise rotation of the cage in relation to control gear 20.

Clockwise rotation of the cage rotates driven spur gear I2, and hence the final driven gear I4, in a clockwise direction.

When the braking of drum 29, for any given load, is sufiiciently increased to overcome the rotational tendency imparted to the drum by the tendency of the cage to rotate anticlockwise, the drum and control gear 29 become locked and hence all rotation of the idlers I9, I 9 is expended in walking around the locked control gear 20. This rotates the cage clockwise to the full extent, and the maximum clockwise rotation is imparted to driven spur gear I2 by planet gears I6, I8. This is the top gear condition.

It is the cage rotation itself which rotates driven spur gear I2, and the maximum (direct) drive would be attained with planet shafts I1, I! looked in relation to the cage. As, however, these planet shafts must rotate anticlockwise in the cage to rotate idlers I 9, I 9 and so rotate the cage about the control gear 20, this very anticlockwise rotation of planet gears I6, I6 cause them to walk anticlockwise on driven spur gear I2, and so permit the latter to rotate more slowly than driving spur gear I I.

With the construction shown in the drawings where gears 18, I9 and 20 are of the same diameter, this anticlockwise rotation of planet shafts I '1 consists of only one revolution in the cage per complete revolution of the cage. With a cnsiderable difference of diameter between planet gears I6 and driven spur gear I2, the automatic top gear condition would fall short of a direct drive only by a limited extent. This difierence from direct drive can be minimised or even eliminated by increasing the ratio of the drive from gears I8 to idlers I9, with a fixed size of control gear 20. Such increase will rotate the idlers faster, and hence rotate the cage further for each revolution of the planet shafts.

It will therefore be observed that the transmission ratio aiforded by the device will automatically vary extensively as follows:

In one extreme condition where no restraint is imposed against the rotation of control drum 29 (and hence against the rotation of planet shafts I1, 11) the cage will rotate freely anticlockwise, and the gears I6 will walk freely anticlockwise about driven spur gear I2. In the other extreme condition wherein drum 29 is completely restrained, a very high transmission speed ratio is achieved.

In the intermediate conditions, the variable degree of restraint imposted on drum 29 determines (for any fixed load) the transmission speed ratio achieved. Conversely, with a fixed resistance to the rotation of drum 29 and a variable load, the device will automatically select the transmission speed ratio necessary to overcome the load, and will always strive to achieve the top gear condition becausethe restraint of the control drum and control gear causes the cage to tend to rotate with driving spur gear Hand hence transmit maximum rotation to driven spur gear I2 and final drive gear I4.

In the intermediate conditions: Where the load is greater than the braking force on drum 29, there will be some anticlockwise rotation of control gear 20 and of the drum and also some clockwise rotation of the cage, yielding a transmission speed ratio less than top gear. As the load falls off, the speed of clockwise rotation of the cage is increased, and when the load is reduced below the braking force, the drum 29 and control gear 20 are halted and the top gear condition is achieved.

The direct drive condition, wherein the reduction gear is ineffective, is achieved by operating lever 32 to move shaft 6 axially and so engage the dogs 36 'of spur gear II with recesses 31 of spur gear l2. In this condition the cage rotates as a unit with driving shaft 6.

The ratchet drive 22, 23 serves the purpose of precluding wasteful rotation of the control gear (worm wheel 24 and Warm 25) in the direct drive condition and also when the driven shaft I3 over-runs the driving shaft 6. To limit the lowest reduction ratio available to a positive figure, it is necessary only to restrain the cage against anticlockwise rotation, as by a ratchet de'vic'e similar to 22, 23. This then fixes the maximum reduction to that provided by the gears I6 to I2.

The application of the reduction gear to v'ari ous uses will be obvious to those skilled in the art, and the auxiliary equipment necessary or de= sirable for such applications is therefore not described.

I claim:

1. A variable ratio gear drive comprising a driving shaft fitted witha driving spur gear, a driven shaft co-axial with the driving shaft but capable of rotation independently thereof and fitted with a driven spur gear, a cage rotatable co-axially with said driving and driven shafts and envelop-- ing said spur gears, a planetary shaft rotatab'ly mounted in said cage and providing a reduction gear connection between the driving and driven spur gears, a control gear co-axial with the driving shaft, a back drive to said control gear consisting of a gear mounted on said planetary shaft and connected to said control gear through an idler gear, a rotatable control mechanism connected to said control gear, and brakin means connected to said control mechanism to impede the rotation of the control gear to cause the cage to rotate in the same sense as the driving shaft.

2. A variable ratio drive according to claim 1, in which the idler gear is rotatably mounted on the cage.

3. A variable ratio drive according to claim 1, in which the idler gear drives the control gear in the sense opposite to that of the driving gear, and including a reduction gear connection between the control gear and the control mechanism.

4. A variable rati'o gear drive according to claim 1, in which the idler gear drives the control gear in the sense opposite to that of the driving gear, and including a reduction gear connection incorporatin a one-way drive between the control: gear and the control mechanism.

5. A variable ratio gear drive comprising a driving shaft fitted with a driving spur wheel, a driven shaft co-axial with the driving shaft but capable of rotation independently thereof and fitted with a driven spur gear, a cage rotatably mounted about said driving and driven shafts and enveloping said spiir gears, two planetary shafts rotatably and symmetrically mounted in said cage non-axially with said driving and driven shafts, two gear wheels mounted on each of said planetary shafts, and connecting the driving spur gear with the driven spur gear with a reduction ratio, a control gear rotatably mounted about the driving shaft, a back drive to the control gear comprising on each planetary shaft a gear exterior of the cage and connected to the control gear through an idler gear mounted on the cage, a rotatable control member connected to and driven by the control gear, and braking means coupled to said control member.

6. A variable ratio gear drive according to claim 5, and including a detachable couplin between the driving and driven shafts.

7. A variable ratio gear drive according to claim 5, and including a detachable dog clutch coupling between the driving and driven shafts,

and a lever connected to the driving shaft to engage and disengage said dog clutch connections.

HECTOR CHARLES COOMBES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date -Re. 18,842 Richards May 30, 1933 694,370 Gill Mar. 4, 1902 1,207,767 Kennedy Dec. 12, 1916 15 2,199,993 Hale May 7, 1940 FOREIGN PATENTS Number Country Date 117,125 Germany Feb. 1, 1901 

